Known axles enable their wheels to rotate independently either:
by means of a single electric motor ("single-motor" axle) by using a mechanical differential and a bevel gear set both of which are mounted in a stepdown gear assembly; or PA1 with one electric motor per wheel ("two-motor" axle). PA1 use of a stepdown gear assembly enabling the traditional solid shaft to be omitted; and PA1 an architecture that is compact and balanced around the axis of the axle. PA1 the motors are rigidly mounted on the axle assembly or they are mounted to float relative thereto; PA1 motion is transmitted between motor and wheel via two separate stepdown gears; PA1 the link between motor and first stepdown gear is implemented: PA1 the mechanical link between the two stepdown gears is provided for each wheel by a "wheel shaft" whose axis coincides with the axis of the wheel; PA1 the link between wheel shaft and wheel is implemented for each wheel by means of the second stepdown gear having a plane or conical epicyclic gear train; PA1 the non-rotary axle shaft and the axle frame are implemented by the stepdown gear assembly on which the suspension rests; PA1 the suspension of the axle is implemented by a single stage only by means of two pneumatic cushions or metal springs, or rubber-metal springs; PA1 the suspension of the axle can accommodate angular displacements relative to the body or the corridor connection of the vehicle, thereby making it possible to omit the load-bearing cross-member and the ball-bearing ring; PA1 braking is provided by disks on the axle or on the driving shafts; PA1 the suspension members and the braking members are disposed between the wheels, thereby making it possible to remove any resilient tires without removing other members; PA1 when the brake disks are on the axle, said brake disks may be in two portions so as to facilitate removal; PA1 the drive, the anti-galloping, and the angular positioning of the axle relative to the body or the corridor connection of the vehicle are implemented by a linkage comprising longitudinal links; and PA1 roll relative to the body or the corridor connection of the vehicle is prevented by an anti-roll bar.
The first solution makes use of a bevel gear set stepdown gear assembly taken from the technology applied to heavy goods vehicles. That solution offers the advantage of grouping together in a single member (the back axle assembly) all of the transmission members (gears) together with the load-bearing structure of the axle, thereby enabling the traditional solid shaft to be omitted.
As a result of the bevel gear set, such a solution suffers from the major drawback of installing the motor perpendicularly to the axis of the axle with a large amount of overhang.
The motor is then supported by a frame, equivalent to a bogie underframe, and is isolated from stresses coming from the track by interposing a suspension stage equivalent to a primary suspension between said frame and the axle assembly. That overhang adversely affects the compactness and the general balance of the axle.
The second solution uses a motor and a stepdown gear for each wheel. By placing each drive-and-gearbox unit on either side of axis of the axle, that solution offers the advantage of eliminating the overhang of the single motor in the above configuration, and thus of procuring a balanced assembly.
Unfortunately the second solution no longer enables the transmission members (gears) to be integrated into a single member (the axle assembly) together with the load-bearing structure of the axle.
The second solution thus does not enable the traditional solid shaft to be omitted, and, given the space taken up by the motors and the stepdown gears placed between the wheels, it makes it necessary to position the suspension systems outside said wheels and therefore requires a braking system using fast disks or shoes on the driving shafts.
Thus, with known solutions, the choice of the type of axle motorization (single-motor or two-motor) results in opting between two significantly different architectures without the chosen architecture being able to enjoy the cumulative advantages of both of the types.